U.S. Pat. No. 4,408,972 was issued Oct. 11, 1983 for an invention entitled "Improvements In Centrifugal Pelletizers and Methods of Centrifugally Pelletizing" by James D. Layfield on behalf of the present assignor, is directed to methods and apparatus for forming pellets of thermoplastic materials, such as polystyrene, polyethylene, polyvinylchloride, and polypropylene, for example. The machine described in the aforementioned application utilizes centrifugal force to extrude the polymer through die holes in a cylindrical rotor die, operating in the range 2000 to 4000 r.p.m., and cuts the polymer strands as they are extruded into pellets which are passed to a quenching water spray.
In the system described, the compounder that incorporates additives into the polymer can increase production, as compared to previous pelletizing machines, without increasing energy consumption, or can reduce energy costs without sacrificing output. For example, a 22 KW unit of the type indicated is capable of the same production rates as a 55 KW extruder/underwater pelletizer, and this power savings become even more pronounced as the capacity of the units is increased.
The present invention is especially directed to improvements in pelletizers of this type wherein the centrifugal head developed in the rotary polymer melt extruder is used to generate the pressure required for extrusion, and the extruder is self-emptying.
In systems of this type, an eddy current heating system can be efficiently and economically employed to add heat to the material and compensate for heat loss.
A prime object of the present invention is to provide an improved feed distribution system to enhance the uniform distribution of the polymer to the rotor and avoid imbalances in feeding which would tend to cause rotor vibration and deleteriously affect the machinery.
Another object of the invention is to provide a more balanced feed system which avoids the transmission of vibration to the cutting blade and keeps the size of the pellets being cut within the proper limits of uniformity which are required.
Still another object of the invention is to provide a magnet powered heating system which utilizes temperature sensors to control the supply of current to the magnets.
Still another object of the invention is to provide a construction which permits quick access to the rotor housing without interfering with the conduction of the magnetic lines of flux.